In recent years, keyboard encoders have been increasingly made from microcomputers because of their numerous advantages including decreasing the number of components, ability to offer many functions and serve extensive applications. However, encoders sometimes malfunction due to external noise, such as static electricity, regardless of whether they use conventional or special purpose ICs or consist of microcomputers.
Especially in case of microcomputerized encoders, which use programs, external noise or the like may sometimes cause the programs to jump out of the intended control loop. Once out of control, the keyboard does not perform its functions at all, and it is not possible for the ordinary user to return the computer program to its original state without switching the power source off. Thus, these encoders are affected seriously by external noise or the like.
More specifically, external noise or the like changes the contents of a program counter acting in a microcomputer to control the reading of program instructions, so that the order in which the program is read changes, thus making the proper execution of the program unfeasible. In this way, a so-called "run away program" is created and the keyboard will not respond to user requests.